Here's a fun stat for you from Pro Football Focus.
Chris Ivory has 57 touches from scrimmage. He has forced 21 missed tackles. That gives him an average of .36 missed tackles missed per touch.
DeMarco Murray has 108 touches and 31 missed tackles for an average of .28.
Marshawn Lynch has 60 touches and 20 missed tackles for an average of .33.
Arian Foster has 74 touches and 15 missed tackles for an average of .20.
Leveon Bell has 91 touches and 23 missed tackles for an average of .25.
Chris Johnson has 49 touches and 7 missed tackles for an average of .14.
Now keep in mind this is not the holy grail of running back stats. You have to consider whether backs can explode through holes. How far can they take it in open field? Can they pass protect? How are their hands? The backs who get more touches are also more productive. It's easier to produce when you take less of a pounding or are better rested.
Still, the ability to create one's own yardage is an important measure of a back, one that perhaps doesn't get enough attention. Pound for pound (touch from scrimmage for touch from scrimmage?) Ivory has been one of the most effective backs in the league through the first quarter of the season. I'll leave it up to you to decide whether Ivory has been better than the other backs listed.
That is aside from Johnson. He's been better than Johnson. Give the ball to Ivory a lot more than you give it to Chris Johnson, Jets.